samples/code_relocation_nocopy: Increase fake flash size

When linking with the 0.16.3 SDK version of picolibc, using long long
cbprintf support pulls in the full floating point printf which is much
larger than the integer-only version. This ends up overflowing the memory
region available for it. Increase the size of that by bumping the start of
the fake region by 8kB.

Signed-off-by: Keith Packard <keithp@keithp.com>